Avoiding unnecessary medical complications or death by ensuring a drug is efficacious for the patient and that the patient is compliant and persistent with their prescription(s) represents a major unmet need and a trillion-dollar global market opportunity—this is larger than the global pharmaceutical industry. As an example, according to Express Scripts, the largest pharmacy benefit manager in the United States, only 25 to 30 percent of medications are taken per the prescriber's instructions (adherence) . . . and of those taken, only 15 to 20 percent are refilled per the prescriber's instructions (persistence). This lack of adherence and persistence is estimated to result in excess of $300 billion being wasted annually for the treatment of unnecessary medical complications in the United States.
Drug-related hospitalizations account for 2.4 to 6.5 percent of all medical admissions in the general population. A meta-analysis found a fourfold increase in the rate of hospitalization related to adverse drug events (ADE) in older adults compared with younger adults (16.6 versus 4.1 percent). A number of factors in older individuals contribute to their increased risk for developing a drug-related problem. These include frailty, coexisting medical problems, memory issues, polypharmacy, and the use of non-prescribed medications. Estimates indicate that 88 percent of the ADE hospitalizations among older adults were preventable, compared with 24 percent among young persons
Optimizing drug therapy is an essential part of medical care. The process of prescribing a medication is complex and includes (i) deciding that a drug is indicated, (ii) choosing the best drug, (iii) determining a dose and schedule appropriate for the patient's physiologic status, (iv) monitoring for effectiveness and toxicity, (v) educating the patient about expected side effects, and (vi) indications for seeking consultation.
Avoidable adverse drug events are the serious consequence of (i) inappropriate drug prescribing, (ii) changes in the patient's reaction to the drug over time due to lifestyle, other medications, other medical conditions, worsening medical condition, or changes in the patients overall well-being, etc., or (iii) addition of new prescription or OTC medications, vitamins, dietary supplements, herbal medicines (e.g., ginseng, Ginkgo biloba extract, glucosamine, St. John's wort, echinacea, garlic, saw palmetto, kava, and valerian root), and/or recreational drugs, etc. Often, clinicians do not question patients about use of herbal medicines and patients do not routinely volunteer this information. Furthermore, most patients do not inform their clinician that they were using unconventional and/or recreational medications. A study of the use of 22 supplements in a survey of 369 patients aged 60 to 99 years found potential interactions between supplements and medications for ten of the 22 supplements surveyed. As a result, any new symptom should first be considered to be drug-related until proven otherwise.
Prescribing for older patients, who consume the most medications per capita, presents unique challenges. Premarketing drug trials often exclude geriatric patients and approved doses may not be appropriate for older adults. Many medications need to be used with special caution because of age-related changes in pharmacokinetics (i.e., absorption, distribution, metabolism, and excretion) and pharmacodynamics (the physiologic effects of the drug).
Larger drug storage reservoirs and decreased clearance prolong drug half-lives and lead to increased plasma drug concentrations in older people. Particular care must be taken in determining drug dosages. The proportional increase in body fat relative to skeletal muscle that generally accompanies aging may result in the increased volume of drug distribution. Decreased drug clearance may also result from the natural decline in renal function with age, even in the absence of renal disease.
The same dose could lead to higher plasma concentrations in an older, compared to younger, patient. For example, the volume of distribution for diazepam is increased, and the clearance rate for lithium is reduced, in older adults. From the pharmacodynamic perspective, increasing age may result in an increased sensitivity to the effects of certain drugs, e.g., benzodiazepines and opioids.
The use of greater numbers of drug therapies has been independently associated with an increased risk for an adverse drug event, irrespective of age, and increased risk of hospital admission. Polypharmacy is of particular concern in older people who, compared to younger individuals, tend to have more disease conditions for which therapies are prescribed. Approximately half of the patients taking drugs take two medications and 20 percent five or more. As an example, one study found that among ambulatory older adults with cancer, 84 percent were receiving five or more and 43 percent were receiving 10 or more medications.
The risk of an adverse event due to drug-drug interactions is substantially increased when multiple drugs are taken. For example, the risk of bleeding with warfarin therapy is increased with coadministration of selective and non-selective NSAIDs, SSRIs, omeprazole, lipid-lowering agents, amiodarone, and fluorouracil. A study found hospitalizations for hypoglycemia was six times more likely in patients who had received co-trimoxazole. Digoxin toxicity was 12 times more likely for patients who had been started on clarithromycin. Hyperkalemia was 20 times more likely for patients who were treated with a potassium sparing diuretic.
Periodic evaluation of a patient's drug regimen is an essential component of medical care. However, a survey of Medicare beneficiaries found that more than 30 percent of patients reported they had not talked with their doctor about their different medications in the previous 12 months. Furthermore, when these reviews are done, they often overlook OTC, supplements, herbal medicines and recreational drugs that are being taken by the patient.
Multiple factors contribute to the appropriateness and overall quality of drug prescribing. These include avoidance of inappropriate medications, appropriate use of indicated medications, monitoring for side effects and drug levels, avoidance of drug-drug interactions, and involvement of the patient and integration of patient values. Current measures of the quality of prescribing generally focus on one or some of these factors, but rarely on all.